Aliphatic ethers, especially polyethers, are commonly employed in end-use applications requiring exposure to high temperatures for extended periods of time. However, the general susceptibility of aliphatic ethers to thermal and oxidation degradation due to the inherently unstable nature of the ether bond has somewhat limited such uses due to the tendency of aliphatic ethers to evolve volatile decomposition products at high service temperatures.
For example, esterified alkoxylated polyols have recently been proposed for use as reduced calorie fat substitutes (as described in U.S. Pat. No. 4,861,613). Although esterified alkoxylated polyols may be readily incorporated into baked goods or in foods such as salad dressing or ice cream which do not require heating, such materials show signs of instability in pan frying or deep fat frying applications. Of the many tests available for measuring thermal stability, the one that has been found most useful for comparing the stability of esterified alkoxylated polyols with that of conventional edible oils is weight loss over time at a constant temperature. This is a useful test from a practical standpoint since cooking oils or fats will last longer and need less-frequent replenishing if weight loss can be minimized. The same weight loss problem may also be observed to a lesser extent in baking or other cooking techniques employing lower temperatures than frying. Although decomposition is expected to be less pronounced at lower temperatures, enhanced stabilization is still highly desirable.
Similarly, polyethers such as polypropylene glycol and ethylene oxide/propylene oxide copolyether polyols are often utilized as lubricants, hydraulic fluids, heat transfer media, or other types of functional fluids. Polyether functional fluids are typically subjected to high temperatures for extended periods of time and thus require stabilization against thermal degradation.